In this study of the relationship of air pollution to asthma, we propose to test preliminary results (for four months in 1970) which indicate that daily visits to emergency rooms for asthma in two large hospitals in the Bedford-Stuyvesant area in Brooklyn, are significantly correlated with daily levels of sulfur dioxide measured in their vicinity. This correlation was not found to hold in Harlem. We propose to enlarge our study to cover the full three year period for which we have collected data. We further wish to include comparable data from Metropolitan Hospital in East Harlem. Clustering of asthma patients in specific geographic areas will also be investigated. The research strategy was designed so that time, season, racial and socioeconomic status are controlled for by the cross sectional comparison at each point in time between the two inner city areas of Bedford-Stuyvesant in Brooklyn and Harlem in Manhattan.